Norway has detected a third Omicron case in a person who tested positive following a company Christmas party in the capital, Oslo.
The Nordic country detected its first two cases on Wednesday.
"At the moment one person is confirmed as infected with Omicron but more cases are expected," Oslo authorities said in a statement.
"We are working actively with contact tracing to limit the spread and prevent bigger outbreaks."
Norway posted a single-day record of 4,052 coronavirus cases on Monday, according to data from the Norwegian Institute of Public Health.
Prime minister Jonas Gahr Stoere is expected to hold a news conference later in the day.
On Tuesday, Stoere urged Norwegians to wear face masks in crowded places and the speeding-up booster vaccinations in the hope of avoiding a new lockdown.
He stopped short of issuing mask mandates, as called for by some municipalities.
Some 88 per cent of adults in Norway, and 71 per cent of all Norwegians, are fully vaccinated. Some 11 per cent of Norwegians have received a booster shot.